Reduced pressure treatment system having a dual porosity pad

ABSTRACT

A wound closure system and method having a porous pad for providing a reduced pressure to a tissue site is disclosed. The porous pad comprises a porous material formed by spraying a chemical substance that cures to form the porous material which has a body and an outer surface. Both the body and the outer surface have pores wherein the average size of the pores in the outer surface is smaller than the average size of the pores in the body. The porous pad further comprises a pathway formed within the porous material that is adapted to fluidly communicate with a source of reduced pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/323,131 filed Dec. 12, 2011, which is a continuation of U.S. patentapplication Ser. No. 12/491,419 filed Jun. 25, 2009, now U.S. Pat. No.8,096,979 issued Jan. 17, 2012, which is a divisional of U.S. patentapplication Ser. No. 11/803,117 filed May 11, 2007, now U.S. Pat. No.7,758,554 issued Jul. 20, 2010, which is a continuation of U.S. patentapplication Ser. No. 10/600,061 filed Jun. 20, 2003, now U.S. Pat. No.7,722,582 issued May 25, 2010, which is a continuation of U.S. patentapplication Ser. No. 09/545,339 filed Apr. 7, 2000, now U.S. Pat. No.6,695,823 issued Feb. 24, 2004, which claims the benefit of U.S.Provisional Application No. 60/128,567, filed Apr. 9, 1999, and anyamendments thereof. All of the above-referenced applications are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the healing of wounds and, moreparticularly, but not by way of limitation, to methods, articles, andsystems for closing wounds that is compact, self-contained, and includesa disposable wound fluids canister and a porous pad, which isbiocompatible with the wound tissue to facilitate the healing of wounds,but does not adhere to the healing tissue.

2. Description of Related Art

Wound closure involves epithelial and subcutaneous tissue adjacent tothe wound migrating towards the center of the wound until it closes.Unfortunately, closure is difficult with large wounds or wounds thathave become infected. In such wounds, a zone of stasis (i.e. an area inwhich localized swelling of tissue restricts the flow of blood to thetissues) forms near the surface of the wound. Without sufficient bloodflow, the epithelial and subcutaneous tissues surrounding the wound notonly receive diminished oxygen and nutrients, but are also less able tosuccessfully fight bacterial infection and, thus are less able to closethe wound naturally. Such wounds have presented difficulties to medicalpersonnel for many years.

The most common technique for closing open wounds has been the use ofsutures or staples. Although such mechanical closure techniques arewidely practiced and often effective, they suffer a major disadvantageby providing tension on the skin tissue adjacent the wound. That is, thetensile force required to achieve closure using sutures or staplescauses very high localized stresses at the suture or staple insertionpoint. Such stresses commonly result in the rupture of the tissue atthose points, which can eventually cause dehiscence in wounds, providingadditional tissue loss.

Moreover, some wounds harden and inflame to such a degree due toinfection that closure by stapling or suturing is not feasible. Woundsnot reparable by suturing or stapling generally require prolongedhospitalization with its attendant high cost, and major surgicalprocedures, such as grafts of surrounding tissues. Examples of woundsnot readily treatable with staples or sutures include large, deep, openwounds; decubitus ulcers; ulcers resulting from chronic osteomyelitis;graft site wounds; and partial thickness burns that subsequently developinto full thickness burns. The use of skin grafts in these situationscan result in the encapsulation of bacteria and other impurities.

One solution to the problem of non-healing wounds has been demonstratedby applying a continuous negative pressure to the wound over an areasufficient to promote migration of epithelial and subcutaneous tissuetoward the wound. A porous pad or other manifolding device may be usedto distribute reduced pressure to the wound. The porous pad typicallycontains cells or pores that are capable of distributing reducedpressure and channeling fluids that are drawn from the wound. Onedrawback, however, to current designs is that new tissue growth mayeasily penetrate the cells or pores and effectively attach the pad tothe wound. Upon removal of the pad from the wound, any tissue in-growththat has occurred must be physically separated from the pad. Typically,the pad removal involves tearing of new tissue, which not only disruptsthe healing process but also may cause discomfort to the patient.

SUMMARY

The problems presented by existing treatment systems are solved by thesystem, articles and methods of the present invention. In accordancewith one embodiment of the present invention, a method for providing areduced pressure to a tissue site is provided. The method comprisesspraying a chemical substance that cures to form a porous materialhaving a body and an outer surface. Both the body and the outer surfacehave pores wherein the average size of the pores in the outer surface issmaller than the average size of the pores in the body. A portion of theouter surface is substantially conformable to the shape of the tissuesite. The method further comprises providing a pathway for the reducedpressure to the porous material.

In another embodiment, providing a pathway for the reduced pressure tothe porous material comprises inserting one end of a tube within theporous material prior to the chemical substance being cured. The otherend of the tube is adapted to fluidly communicate with a source ofreduced pressure.

In yet another embodiment, providing a pathway for the reduced pressureto the porous material comprises positioning one end of a tube adjacentthe tissue site while spraying the chemical substance. One end of thetube is contained within the porous material after the chemicalsubstance cures, and the other end of the tube is adapted to fluidlycommunicate with a source of reduced pressure.

In yet another embodiment, a porous pad for providing a reduced pressureto a tissue site is provided. The porous pad comprises a porous materialformed by spraying a chemical substance that cures to form the porousmaterial having a body and an outer surface. Both the body and the outersurface have pores wherein the average size of the pores in the outersurface is smaller than the average size of the pores in the body. Aportion of the outer surface is substantially conformable to the shapeof the tissue site. The porous pad further comprises a pathway formedwithin the porous material that is adapted to fluidly communicate with asource of reduced pressure.

In yet another embodiment, the chemical substance comprises apressurized liquid before being sprayed. The chemical substance expelsgas from the pressurized liquid when sprayed so that the chemicalsubstance expands and hardens to form the porous material.

In another embodiment, a tissue treatment system is provided. The systemcomprises a porous material formed by spraying a chemical substance thatcures to form the porous material having a body and an outer surface.Both the body the outer surface have pores wherein the average size ofthe pores in the outer surface is smaller than the average size of thepores in the body. A portion of the outer surface is substantiallyconformable to the shape of the tissue site. The system furthercomprises a pathway formed within the porous material that is adapted tofluidly communicate with a source of reduced pressure whereby reducedpressure is provided to the tissue site. The system further comprises aconduit operable to deliver the reduced pressure with a first end of theconduit being connectable to the pathway and a second end of the conduitbeing connectable to the source of reduced pressure.

Other objects, features, and advantages of the present invention willbecome apparent with reference to the drawings and detailed descriptionthat follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting the vacuum pump unit of a woundclosure apparatus constructed according to the teachings of the presentinvention.

FIG. 2 is a right side plan view depicting the vacuum pump unit of FIG.1.

FIG. 2A is a detail view of the latch 26 portion of FIG. 2, partiallycutaway to eliminate guide (or key) 29 from the view and to showportions of latch 26 in sagital cross section.

FIG. 3 is a perspective view depicting a wound drainage collectioncanister for use in conjunction with the vacuum pump unit of FIG. 1.

FIG. 4 is a rear plan view depicting the wound drainage collectioncanister of FIG. 3.

FIG. 5 is a perspective view depicting the connection of a wounddrainage collection canister of FIG. 3 to a wound coverage pad.

FIG. 6 is a front plan view in partial cross section depicting theconnection of the wound drainage collection canister of FIG. 3 withinthe housing of the vacuum pump of FIG. 1.

FIG. 6A is a partial view of the apparatus shown in FIG. 6 except thecanister is removed.

FIG. 7 is a perspective view depicting the filter carrier of the wounddrainage collection canister.

FIG. 8 is a top plan view depicting the filter cap of the wound drainagecollection canister.

FIG. 9 is a schematic view depicting the control system for a woundclosure apparatus constructed according to the teachings of the presentinvention.

FIG. 10 is a section through a wound showing the wound pad in place.

FIG. 11 is a porous wound pad being dipped into a solution.

FIG. 12 is a porous wound pad with varying porosity on two sides (withtube).

FIG. 13 is a side of a porous wound pad being melted by a heat source.

FIG. 14A is a cross section of chemical being sprayed into the wound.

FIG. 14B is a cross section of chemical being sprayed into the wound(with tube).

FIG. 15 is a cross section of a wound where spraying of the chemical hasbeen completed (with tube).

FIG. 16 is a cross section of a wound where the sprayed chemical hashardened into the contours of the wound (with tube).

FIG. 17 is a porous sock wrapped around the porous wound pad (withtube).

FIG. 18 is a porous wound pad with a removable micropore layer (withtube).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As illustrated in FIGS. 1 and 2, front housing 11 and rear housing 12connect together using any suitable means such as screws and fastenersto provide wound closure vacuum pump 10 with a small, compact, andeasily portable carrying case. Consequently, front housing 11 and rearhousing 12 connect together to form handle 13 that permits easy carryingof the wound closure apparatus 10. Except as may be otherwise evidentfrom this description, the carrying case of the vacuum pump 10 issubstantially as described and shown in WIPO Design No. DM/032185.

Front housing 11 includes power switch 15 that is movable between an onand off position to permit user control of the delivery of power to thewound closure apparatus 10. Keypad 16 and liquid crystal display (LCD)17 mount to front housing 11 to permit the programming of the woundclosure apparatus 10. Chamber 18 is defined by integrally formedinterior side walls 100 and 101, top wall 102, bottom wall 103 and rearwall 104. Side wall 100 is dependently attached to the interior of thefront housing 11 by standard mounting hardware (not shown). The woundfluids collection canister 19, illustrated in FIGS. 3-5, is receivedwithin chamber 18. Side walls 100 and 101 each include a key 29 and 30,respectively, that aid in the alignment of wound fluids collectioncanister 19 within chamber 18. Furthermore, front housing 11 includeslatch 26 to secure the wound fluids collection canister 19 withinchamber 18.

Rear housing 12 includes arm 14 pivotally mounted to it within recess110. An identical arm pivotally mounts to the opposite side of rearhousing 12 within an identical recess. Arm 14 and its corresponding armmounted on the opposite side of the rear housing 12 pivot from withintheir recesses to a position where they support the wound closureapparatus 10 at an angle. Arm 14 and its corresponding arm angularlysupport the wound closure apparatus 10 to permit easier user access tokeypad 16. Arm 14 and its corresponding arm may also be used to permithanging of apparatus 10 from a hospital bed foot board.

Canister 19 has a shape as shown in FIGS. 3 to 6. As illustrated inFIGS. 3 to 6, canister 19 includes side walls 20 and 21, top wall 23,bottom wall 24, back wall 22 and front wall 25 that define therectangular chamber for receiving blood, pus, and other fluids emittedfrom a wound. Side walls 20 and 21 include key ways 27 and 31respectively, that receive a respective one of keys 29 and 30 to provideeasy alignment of canister 19 within chamber 18. Furthermore, key way 27includes recess 28 that receives latch 26 to fasten canister 19 withinchamber 18

Front wall 25 of canister 19 includes raised portion 32 extendingtherefrom to furnish a window that permits a user to determine the levelof wound fluids within canister 19. Accordingly, raised portion 32 istransparent so that the level of wound fluids within canister 19 may bevisually determined. Raised portion 32 includes side walls 110 and 111,top wall 112, bottom wall 113, and front face 114 that define a chamberwhich opens into the chamber defined by side walls 20 and 21, top wall23, bottom wall 24, back wall 22 and front wall 25 of canister 19. Frontface 114 of raised portion 32 includes graduations that demarcate thevolume of wound fluid within canister 19. Additionally, side walls 110and 111 of raised portion 32 include ridges that provide a grippingsurface for the user during the insertion and removal of canister 19from chamber 18.

Although raised portion 32 is transparent to permit the determination ofthe level of wound fluids within canister 19, side walls 20 and 21, backwall 22, top wall 23, bottom wall 24, and front wall 25 are opaque sothat they are only translucent. As an alternative, the portions ofcanister 19 surrounding filter 46 may also be transparent. This enablesa user to visually check for signs of contamination of filter 46. Inthis preferred embodiment, side walls 20 and 21, back wall 22, top wall23, bottom wall 24, front wall 25, and raised portion 32 of canister 19are fabricated from a plastic material.

Canister 19 includes inlet 35 that is formed integrally with top wall112 of raised portion 32. Inlet 35 is cylindrical in shape andcommunicates with the interior of canister 19 to permit the transfer ofwound fluids into canister 19. In this preferred embodiment, inlet 35 isalso fabricated from a plastic material.

In order to prevent liquids sucked into the canister 19 from splashingdirectly onto cap 49, which mask the outlet 44, and to reduce foamingwithin the canister 19, inlet 35 has a blind inner end. Inlet 35 has aslot 35A so that drainage fluid is deflected downwardly into the raisedhandle portion 32 of the canister 19. Handle portion 32 may communicatewith the main part of the canister 19 through one or more holes in wall25. It is desirable to avoid foaming because this can give a falsereading when a capacitance sensing device is used to sense when thecanister 19 is filled. An anti-foaming material, e.g. a silicone, may beadded to the canister 19, e.g. by coating the interior walls. It mayalso be advantageous to include a gel-forming substance, e.g. apolyacrylamide of modified starch in order to immobilize the drainagefluid. This is particularly useful if the apparatus is likely to betilted.

Wound fluids (i.e. drainage) are communicated through inlet 35 intocanister 19 via pad 36 and hoses 37 and 38. In this preferredembodiment, the portion of the pad 36 next to the vacuum tube 37 (i.e.inner portion or surface) is fabricated from an open cell polyurethaneor polyether foam. The outer surface of the pad 36 in contact with thewound cavity 216 can consist of the same material as the inner portionor surface next to the vacuum tube 37 where the size of the pores is 100microns of less. Hose 37 is inserted within pad 36 by making an incisionin pad 36 and inserting the end of hose 37. Hose 37 can then be securedwithin pad 36 using any suitable means such as an adhesive or a flange.Preferably, the porous pad 36 has an elongated hole 300 (See FIG. 11)for the drainage tube 37 which is an interference fit with the tube 37.The hoses 37 and 38 are preferably made from medical grade PVC tube.Hose 38 mounts within inlet 35 using any suitable means such as adhesiveor welding. Hoses 37 and 38 include luer lock connectors 39 and 40,respectively, (or the equivalent, such as any known quick disconnecttype coupling) that attach together to permit communication betweenhoses 37 and 38. Furthermore, hoses 37 and 38 include pinch clamps 41and 42, respectively, that are capable of sealing their respective hose37 or 38 to prevent the flow of wound fluids. The porous pad 36 ispreferably packaged in a sterile container together with its connectorand clamp. When packaged, the clamps will be in their open condition.

The communication of wound fluids into canister 19 requires the securingof pad 36 over a wound. Pad 36 is secured over a wound using cover 43which is fabricated from a plastic material and includes an adhesive onone side that sticks to human skin. Wound cover 43 is conveniently asurgical drape material comprising a sheet of elastomeric materialcoated peripherally or overall with a pressure-sensitive adhesive, suchas an acrylic adhesive. The elastomeric or rubbery nature of the woundcover 43 is important because it accommodates changes in pressure in thewound area during intermittent operation of the vacuum pump 84. Thewound cover 43 is preferably a polyurethane film with a removablebacking sheet, i.e. of polythene to protect the adhesive surface.

A high degree of reticulation in the inner portion or surface of theporous pad 36 next to the vacuum tube 37 is desirable to achieve goodpermeability when the pad 36 is under suction. The outer surface of thepad 36 next to the wound, however, is smooth and contains pores ofapproximately 100 microns in diameter to allow for vacuum air flowthrough the pad 36 while preventing the healing tissue from crosslinking with the pad 36. While the upper range of pore size is notexactly known, it is between 100 microns and 1000 microns (onemillimeter). The lower end of the pore size is simply large enough toallow air and fluids to flow therethrough which could be as small as onemicron.

There are several different ways to prepare a pad 36 for use with thewound drainage apparatus 10 which contains an outer surface with thepreferred specifications. One way is to make a porous pad 36 out of amaterial which consists entirely of micropores (not shown) with adiameter of approximately 100 microns or less, or blow the pad 36 insuch a way that the portion to be inserted into the wound cavitycontains the micropores of a diameter of approximately 100 microns orless as will be subsequently described. A micropore is an opening in thepad 36 of approximately 100 microns or less.

Referring to FIGS. 11 and 12, a second way to create the pad 36 is todip the portion of the pad 36 which is to be placed inside the wound ina liquid coating material 201 which dries into the pad 36 acting as abulking agent thereby reducing the diameter of the pad pores 205 toapproximately 100 microns or less. This effectively creates a smoothouter surface with a pore size of approximately 100 microns or less,hereinafter called micropores 207, to be placed in the wound cavity 216.An inner surface can have pores 205 of a size of greater than 100microns which have a greater vacuum compatibility with the vacuum tube37.

In FIG. 11, a porous wound pad being dipped into a solution 201 isshown. FIG. 11 shows a porous wound pad 36, with top 203, bottom 204,and side 206. The pores 205 of the porous wound pad 36 are a vacuumcompatible size. A vacuum tube 37 is shown in the side 206 of the porouswound pad 36. The pad 36 is being dipped to approximately 1 millimeterinto a liquid coating material 201, such as a liquid hydrophilic foamsolution, held in a flat tray 202, which when hardened acts as a bulkingagent to form a smooth micropore layer 211 with micropores 207 of adiameter of approximately 100 microns or less. This allows for the flowof negative air pressure and fluids through the pad 36 withoutcompromising the healing tissue surface. The coating of the pad 36 canoccur directly before insertion into the wound cavity 216, allowingenough time for drying, or the pad 36 can be coated duringmanufacturing. Furthermore, for certain types of wounds it may benecessary to mix an antimicrobial agent such as Neosporin with theliquid coating material 201 so as to create a modified pad surface whichis difficult for bacteria to stick to thus preventing bacterialmigration through the pad 36. The addition of the coating to the pad 36does not hamper the ability to trim the pad 36 to conform to the woundcavity 216.

FIG. 12 shows a cross section of a porous wound pad 36 with varyingporosity on one surface (with tube). This varying porosity can resultfrom the porous pad 36, with top 203, bottom 204 and side 206, beingdipped in the liquid coating material 201 as described in FIG. 11. Thispad 36 contains an upper pore layer 212 with vacuum compatible pores 205and a smooth micropore layer 211 with healing compatible pores 207 whichhave a diameter of approximately 100 microns or less. By having a sizeof approximately 100 microns or less, tissue cannot grow into themicropore layer 211. Again the liquid coating material 201 (a) can bemodified with an antimicrobial agent such as Neosporin to deterbacterial migration through the pad 36, or (b) forms a tissue compatiblelubricious surface that is growth factor impregnated or is a moleculargraft.

Referring to FIG. 13, another way of creating the optimum outer padsurface is to take a porous pad 36 with pores 205 that may have adiameter greater than 100 microns and heat that pad 36 on the side to beplaced inside the wound cavity 216 with a heat source 208 so as toshrink or melt the pore size to a diameter of approximately 100 micronsor less while maintaining a smooth texture. In FIG. 13, a side of aporous wound pad being melted by a heat source is shown. The pad 36,with top 203, bottom 204, and side 206 and containing pores 205 ofvacuum compatible pore size, is shown on a hot plate 208. This hot plate208 has a standard current adapter 209 and plug 210. While a hot plate208 was used in this illustration, any heat source could be used. Theheat source 208 was simply necessary to melt the surface of the pad 36partially so as to create a smooth micropore layer 211 with healingcompatible micropores 207 of approximately 100 microns or less.

Referring to FIGS. 17 and 18, the porous pad 36 can be made with asmooth outer surface of approximately 100 microns or less by taking apad 36 with vacuum compatible pores 205 and placing the pad 36 within aporous sock 213 which is smooth and contains pores 207 with a diameterof approximately 100 microns or less. The sock-covered pad 36 is thenplaced inside the wound cavity (not shown in this Figure). FIG. 17 showsa porous wound pad 36 situated within a porous sock 213. The pad 36,with top 203, bottom 204, and side 206, has vacuum compatible pores 205and a vacuum tube 37 for use in extending the negative air pressurethrough the pad 36. The porous sock 213 contains healing compatiblepores 207 of a diameter of approximately 100 microns or less and acts asa covering being placed over the porous wound pad 36 before insertioninto the wound cavity 216. If any trimming of the pad 36 is needed itcan be done before the pad 36 is placed in the sock 213 before insertioninto the wound cavity 216.

Referring specifically to FIG. 18, a variation of the techniquedemonstrated in FIG. 17 would be to affix a smooth porous membrane 219only to the face of the pad 36 that is to be placed into the woundcavity 216. This membrane 219 contains pores of a diameter ofapproximately 100 microns or less. The porous sock 213 or membrane 219may be composed of TEFLON, rayon, or a similar material. Knit rayon filmis often used for conventional dressings to try to accelerate the growthof granulation tissue. The membrane 219 may form a tissue compatiblelubricious surface that is growth factor impregnated and antimicrobial.In FIG. 18, a porous wound pad 36 with a removable membrane 219 isshown. The pad 36, with top 203, bottom 204, and side 206 and vacuumcompatible pores 205, contains a vacuum tube 37 for use in extending thenegative air pressure through the pad 36 for aspiration of the woundcavity 216. The removable membrane material 219, such as Teflon orrayon, contains healing compatible micropores 207 of a diameter of 100microns or less. This membrane material 219 can be placed around theportion of the pad 36 which is to go into the wound cavity 216. Themembrane 219 can be held in place on the pad 36 by any biocompatiblemeans such as an adhesive.

Referring to FIGS. 14 through 16, another way in which the pad 36 ismade is by spraying a nontoxic chemical substance 215 directly into thewound cavity 216. The chemical substance 215 hardens into the shape ofthe wound cavity 216 when placed directly into the wound 216. This formsa pad 36 such that the surface of the pad 36 next to the healing tissueis smooth and has pores of a diameter of approximately 100 microns orless. A chemical substance (not shown) can also be sprayed in a sterileenvironment before insertion into the wound cavity 216. When the pad 36is formed on an external sterile surface it is allowed to hardenslightly into a foam like substance and then pressed into the woundcavity 216 so as to conform to the wound. The chemical substances usedin these circumstances are sprayed so as to make a pad 36 with a smoothouter surface containing pores with a diameter of approximately 100microns or less.

FIG. 14A shows a cross section of chemical being sprayed into a wound. Anontoxic chemical substance 215 is sprayed from the spray nozzle 218 ofa container (not shown). The chemical substance 215 is under pressuresuch that when it is sprayed into the wound cavity 216 of the body 214the gas is expelled from the chemical substance 215 which allows thechemical substance 215 to expand from a liquid phase to a solid porousphase which conforms to the shape of the wound cavity 216 (See FIG. 15where the solidification of the pad 36 is shown with a wound cover 43placed over the pad 36 and tube 37 assembly.). The vacuum tube 37 shouldbe placed in the cavity 216 during the spraying of the chemicalsubstance 215 before solidification occurs (See FIG. 14B). This porouspad 36 which is formed (See FIG. 16) is equally vacuum compatible nextto the vacuum tube 37 as well as compatible with the healing tissuecontaining a smooth surface and only micropores 207 of approximately 100microns of less in diameter in contact with the wound cavity 216.

The type of pad 36 can vary based on the type of wound involved. Inaddition, the type of wound may dictate that an antimicrobial agent,such as Neosporin, be used in the pad 36 entirely or on the surfacewhich is in contact with the wound so as to give a topical antimicrobialeffect.

In use, the porous pad 36 is cut to a size which corresponds closely tothe edge of the wound with the objective of packing the pad 36 into thewound cavity 216 so that it contacts the surface of the cavity 216,rather than bridging the cavity 216. As depicted in FIG. 10, the cavity216 may be extensive and there may be little or no tissue coverage tothe bone 212. This is illustrated diagrammatically in FIG. 10. FIG. 10is a cross-section through a wound showing the porous pad 36 packed inthe wound cavity 216. It is important that the pad 36 should be firmlypacked into the recesses of the wound cavity 216. Drainage tube 37terminates within the center of the porous pad 36. Surgical drape 43extends over the porous pad 36 and is adhered to intact skin around theperiphery of the wound. Drape 43 is also firmly adhered around the tube37 to prevent leakage of air. A wound cover 43 is then adhered to thesurrounding skin and around the drainage tube 37 to provide an air-tightseal around the wound.

As illustrated in FIGS. 2, 4 and 6, canister 19 includes outlet 44 thatmounts over port 45 to permit wound closure apparatus 10 to draw woundfluids into canister 19. Outlet 44 is cylindrically shaped and formed asan integral part of back wall 22 by outer wall 33 and inner wall 50which are interconnected by end wall 34. Passageway 52, defined in partby interior wall 50 and in part by filter cap 49, provides the actualconduit for outlet 44 between the interior and exterior of canister 19.The placement of canister 19 within recess 18 such that outlet 44resides over port 45 couples canister 19 to a vacuum pump 84. The vacuumpump 84 removes air from canister 19 to create a vacuum pressure withincanister 19. That vacuum pressure is then transmitted to a wound sitethrough hoses 37 and 38, thereby not only enabling therapeutic use ofsystem 10, but also tending to promote wound drainage. Any wounddrainage fluid is then drawn through pad 36 and hoses 37 and 38 intocanister 19.

Outlet 44 resides near top wall 23 of canister 19 to ensure efficientoperation of the vacuum pump 84. That is, the vacuum pump 84 removes themost air from canister 19 when the air does not have to first bubblethrough wound fluids contained in canister 19. Consequently, with outlet44 positioned near the top of canister 19, the vacuum pump 84 removesair directly from canister 19, and it is only during the final fillingof canister 19 that air must bubble through wound fluids. Preferably, asdescribed below, the apparatus includes detecting and warning meanswhich operates before the level of drainage fluid reaches either theinlet or outlet tube so that a fresh canister 19 can be installed.

In removing fluids from a wound utilizing wound closure apparatus 10, amajor safety concern is preventing wound fluids from contaminating thevacuum pump 84. Accordingly, filter 46 mounts over outlet 44 utilizingfilter carrier 48 and filter cap 49 to block the flow of wound fluids tooutlet 44 so that wound fluids remain within canister 19 and do not flowinto the vacuum pump 84. In this preferred embodiment, filter 46 is a0.2 micron hydrophobic membrane filter providing a bacterial barrier,although other filters may be substituted as appropriate.

As illustrated in FIG. 7, filter carrier 48 includes face 53 formedintegrally with lip 54. Face 53 includes groove 56 formed therein, whilelip 54 supports brace 55 in its interior. Filter 46 fits within groove56 of face 53 and is supported within filter carrier 48 by brace 55 oflip 54. An O ring 53A is fitted in peripheral recess of filter carrier48 to accommodate manufacturing tolerances and ensure a fluid tight sealwith filter cap 49.

As illustrated in FIGS. 6 and 8, filter cap 49 includes cylindricalportions 57 and 58, which are formed integrally (with annulus 57′spanning there between), to hold filter carrier 48 within passageway 52of outlet 44. To mount filter 46 over passageway 52, filter 46 is firstplaced within filter carrier 48 as described above. Filter carrier 48 isthen positioned within filter cap 49 such that face 53 abuts annulus 57′of filter cap 49 and lip 54 of filter carrier 48 resides within annularlip 50′ of outlet 44. Accordingly, when cylindrical portion 57 of filtercap 49 mounts over outlet 44, the front face 53 of filter carrier 48 andthe outer edges of filter 46 abut annulus 57′ to secure filter 46 withinpassageway 52. Filter cap 49 attaches to outlet 44 using any suitablemeans such as an adhesive or welding. Filter cap 49 is completely sealedexcept for aperture 51 positioned on top of filter cap 49. Aperture 51communicates with port 45 via passageway 52 of outlet 44 to permit thevacuum pump 84 to draw air from the interior of canister 19.

As illustrated in FIGS. 2 and 6, port 45 includes O-ring 59 mountedthereabout to provide a fluid tight seal between port 45 and inner wall50 of outlet 44. Port 45 mounts through rear wall 104 of chamber 18using any suitable means such as nuts 60 and 61. Furthermore, line 62attaches to the rear of port 45 using any suitable means such as a clampto couple port 45 to the vacuum pump 84.

Switch 63 protrudes through rear wall 104 of chamber 18 to produce asignal indicating when canister 19 properly and securely resides withinchamber 18. In this preferred embodiment, switch 63 is a normally openpush button switch that mounts on rear wall 104 of chamber 18 using anysuitable means such as a bracket. When canister 19 is properlypositioned within chamber 18, its rear wall 22 presses the head ofswitch 63, closing switch 63 so that it provides a signal indicatingthat canister 19 properly resides within chamber 18.

Fill sensor 64 resides adjacent side wall 101, exterior to chamber 18.Fill sensor 64 provides a signal that indicates when canister 19 isfilled with wound debris. In this preferred embodiment, fill sensor 64is a capacitive sensor that mounts on side wall 101 of chamber 18 usingany suitable means such as a bracket or appropriate adhesive material.Fill sensor 64 has a sensing profile 64A which determines the point atwhich the capacitance measurement is made. When wound fluids havereached the level within canister 19 which corresponds to the locationof the sensing profile 64A, the capacitance within canister 19as >seen=by fill sensor 64 changes, resulting in fill sensor 64outputting a signal indicating that canister 19 is filled with woundfluids to the level at which the sensing profile is located. Theposition of this sensing profile behind wall 101 can be changed (seeFIGS. 6A) to provide an optimum balance of space and volume utility.

As illustrated in FIG. 2A, latch 26 generally comprises latch pin 65,handle 66, latch guide sleeve 68A and spring 67. Latch pin 65 comprisesa proximal end 65A and distal end 65B. Latch guide sleeve 68A abuts theinner surface of front housing 11 and is held securely in place from theouter side of front housing 11 by nut 68B. Handle 66 screws onto theproximal end 65A of latch pin 65 and is locked in position by nut 69A.In the preferred embodiment, cover 68 over nuts 69A and 68B provides asurface against which handle 66 abuts, thus preventing end 65B fromexcessively entering chamber 18 as will be understood further herein.Cover 68 also provides aesthetic enclosure of nuts 69A and 68B.Dependent attachment of side wall 100 (chamber 18), as described hereinabove, is such that side wall 100 abuts latch guide sleeve 68A on theside distal front housing 11. Further, this arrangement causes distalend 65B of latch pin 65 to project into chamber 18 under the force ofspring 67 (shown partially cut away). Spring 67 residescircumferentially about latch pin 65 within an axial bore of latch pinguide 68A. Spring 67 exerts force between distal end 65B of latch pin 65and an annulus within the axial bore of latch pin guide 68A. Atransverse slot in the distal end of latch pin guide 68A receives end65B of latch pin 65, providing rotational alignment of end 65B andfurther recess for end 65B when a user pulls handle 66 in an axialdirection.

Latch 26 operates to ensure canister 19 remains secured within chamber18. End 65B of latch 26 terminates in a point that protrudes through key29 into chamber 18. During the placing of canister 19 within chamber 18,key way 27 of canister 19 forces the point 65B of the latch pin withinkey 29. However, once canister 19 has been properly positioned withinchamber 18, recess 28 resides below latch pin end 65B so that spring 67biases the point 65B of latch pin 65 into recess 28 to prevent theremoval of canister 19 from chamber 18. The removal of canister 19 fromchamber 18 is accomplished by grasping handle 66 and pulling the point65B of latch pin 65 from recess 28. With the point of latch pin 65 nolonger within recess 28, canister 19 may be pulled from chamber 18 usingits raised portion 32.

As illustrated in FIG. 9, wound closure apparatus 10 preferably plugsinto a standard 115/120 VAC power source (e.g. an outlet) to supplypower to control system 70. Alternative embodiments (not shown, althoughsimilar) are readily adapted for 220 VAC power by changing the powercord and appropriately rewiring the taps of the transformer within DCpower supply 71, as is readily known in the art. The application ofpower to control system 70 is regulated by power switch 15 which is astandard push button on/off switch. With power switch 15 depressed, DCpower supply 71 receives the 115/120 VAC signal and converts it into a12 VDC signal for use by fan 74 and vacuum pump 84. A conventionalvoltage regulator 96 steps down the voltage to +5V for use by each ofthe other DC components 16, 17, 63, 64, 72, and 75. Voltage regulator 96connects to keypad 16, LCD 17, switch 63, fill sensor 64,microcontroller 72, transducer 75, and tilt sensor 82 to supply each ofthem with the +5V DC signal. Microcontroller 72 links to solid staterelays (MOSFETs) 97 and 98 for controlling the provision of the 12 VDCpower supply to fan 74 and pump motor 83, respectively.

As illustrated in FIG. 1, once power switch 15 is depressed, a useremploys keypad 16 and LCD 17 to select the operating parameters forwound closure apparatus 10. Wound closure apparatus 10 stores thepreviously selected operating parameters so that upon powerinitialization, LCD 17 displays the phrase NEW PATIENT with the word NOover arrow button 76, and the word YES over arrow button 77. If the userpresses arrow button 76 to answer no, wound closure apparatus 10 willoperate at the previously selected parameters. After answer no, the userpressures on/off button 78 to begin operation of wound closure apparatus10.

Conversely, if the user presses arrow button 77 to indicate a newpatient, wound closure apparatus 10 will operate either under defaultvalues or allow the user to select the operating parameters. To operateunder default parameters, the user presses on/off button 78 afterpressing arrow button 77. However, to select his or her own values, theuser presses option button 79 after pressing arrow button 77.

Upon the pressing of options button 79, LCD 17 displays a bar graphrepresenting the spectrum of available vacuum pump pressures and anumerical representation of the vacuum pump pressure presently displayedby the bar graph. The user changes vacuum pump pressure using arrowbuttons 76 and 77. The pressing of arrow button 76 reduces vacuum pumppressure, while the pressing of arrow button 77 increases vacuum pumppressure. After selecting the desired vacuum pump pressure, the userpresses option button 79 to save the selected vacuum pump pressure.

Once the selected vacuum pump pressure has been saved, LCD 17 displaysthe pump operation times available to the user. The user may programwound closure apparatus 10 to pump either continuously orintermittently. Thus, LCD 17 displays the word CONTINUOUS over arrowbutton 76 b and INTERMITTENT over arrow button 77. The user selectscontinuous operation by pressing arrow button 76 followed by on/offbutton 78 to activate the vacuum pump 84. In its continuous mode, woundclosure apparatus 10 runs its vacuum pump 84 continuously until on/offbutton 78 is pressed again.

If the user presses arrow button 77 to select intermittent operation,LCD 17 displays a bar graph representing the minimum and maximum ontimes for the vacuum pump 84. LCD 17 also displays the phase ON TIME andthe numerical value presently displayed by the bar graph. A userdecreases the on time of the vacuum pump 84 by pressing arrow button 76and increases the on time of the vacuum pump 84 by pressing arrow button77. After selecting the desired on time, the user presses options button79 to save the selected on time value.

LCD 17 then displays a second bar graph representing the off time forthe vacuum pump 84 with the phrase OFF TIME and the numerical valuepresently depicted by the bar graph. Again, arrow buttons 76 and 77 arepressed to increase or decrease, respectively, the off time for thevacuum pump 84. After selecting the off time, the user presses optionsbutton 79 followed by on/off button 78 to operate wound closureapparatus 10 using the selected parameters.

Keypad 16 includes setting button 80 to permit the user to sequentiallydisplay the currently selected operating parameters of wound closureapparatus 10. Keypad 16 further includes delay button 81 to permit theuser to deactivate an alarm sounded in response to an improper operatingcondition of wound closure apparatus 10. Delay button 81 provides theuser with the ability to silence alarms so that the alarm will not haveto be listened to during the correction of the problem.

Any new alarm conditions occurring within the fifteen minute period(delay period) after the pressing of delay button 81 will not beindicated by an audible alarm. However, the pump will still bedeactivated when appropriate, even during the delay period.

Again referring to FIG. 9, microcontroller 72 is a multi-portmicroprocessor with a ten-bit analog to digital (A/D) converter havingassociated memory that stores the program directing microcontroller 72during its controls of wound closure apparatus 10. After receiving andstoring the user selected operational parameters and receiving an onsignal due to the pressing of on/off button 78, microcontroller 72activates pump motor 83 which, in turn, drives vacuum pump 84 to beginthe removal of air from canister 19.

As vacuum pump 84 operates, it draws air from within canister 19, intoline 62 via outlet 44 of canister 19 and port 45. Line 62 connects tofilter 85 and transducer 75 via T-junction 91. Filter 85 is similar tofilter 46 and thus ensures no wound fluids contaminate vacuum pump 84.Filter 85 communicates with pump 84 via T-junction 88 and one arm of thelatter is connected to bleed valve 86. Bleed valve 86 communicates withthe atmosphere to release pressure developed within line 62 by vacuumpump 84 after microcontroller 72 deactivates vacuum pump 84. Bleed valve86 is sufficiently small to ensure that it generally does not affect thevacuum pressure levels achieved by vacuum pump 84 as it evacuates airfrom canister 19, except to prevent over pressurization beyond 250 mm Hgand to prevent erratic operation of the vacuum pump 84 at very lowpressure settings.

In the preferred embodiment, an orifice of 0.5 mm diameter is especiallypreferred for bleed valve 86. Valve 86 or the equivalent is particularlyimportant for enabling intermittent application of negative pressure, asthe orifice 86 allows for gradual release of the negative pressure (overa period of about fifteen seconds) when the pump motor 83 isde-actuated. Bleed valve 86 is positioned outside housing 11 tofacilitate un-clogging of aperture 86 in the event of a blockage. Anaperture is provided in bleed valve 86, which is machined from stainlesssteel. Flow control orifices would be alternatives.

Line 62 also includes T-connector 91 to connect it with line 92. Line 92is connected to tank 94 which acts as a damper to pressure changes inline 62. This dampening effect, facilitated by restrictor 89 in line 93between transducer 75 and T-junction 91, causes the pressure measured bytransducer 75 to be an accurate indication of actual wound sitepressure. Transducer 75 communicates with line 62 via line 93 to measuretank 94 pressure and produce an electrical signal representative of thatpressure. Transducer 75 outputs its pressure signal to microcontroller72.

Microcontroller 72 utilizes the pressure signal to control the speed ofpump motor 83. As previously described, the user selects either adefault vacuum pump pressure or a desired vacuum pump pressure for theoperation of wound closure apparatus 10. After receiving the woundpressure signal from transducer 75, microcontroller 72 compares thewound pressure with the user selected pressure. If the wound pressure ishigher than the user selected vacuum pump pressure, microcontroller 72reduces pump motor speed to decrease vacuum pump pressure and thus thepressure at the wound. Conversely, if the wound pressure is less thanthe user selected vacuum pump pressure, microcontroller 72 increases thespeed of pump motor 83 resulting in an increase in the vacuum pressureapplied at the wound.

Microcontroller 72 controls pump motor 83 by varying the amount ofvoltage received by pump motor 83. That is, microcontroller 72 receivesthe 12 VDC signal from DC power supply 71 and outputs a voltage between0 and 12 VDC to pump motor 83 to control its speed in accordance withthe user selected vacuum pump pressure value. Accordingly,microcontroller 72 employs feedback to ensure that the wound experiencesthe user selected vacuum pump pressure. If the target pressure is notreached after a period of five minutes, microcontroller 72 deactivatesmotor 83 and sounds the audible alarm. Additionally, the feedback signalprevents maximum vacuum pump pressure from being exceeded. If the woundpressure measured by transducer 75 exceeds a maximum safe vacuum pumppressure microcontroller 72 deactivates pump motor 83 and activatesalarm 95 to signal a malfunction.

Wound closure apparatus 10 includes fan 74 to cool pump motor 83 andprinted circuit (PC) board 200 during the operation of the wound closureapparatus 10. In the preferred embodiment, microcontroller 72 controlsfan 74 to always operate while power is being supplied. In alternativeembodiments, however, microcontroller 72 controls fan 74 to operate onlyin relation to motor 83, because it is only necessary for fan 74 tooperate if motor 83 is also operating. In such alternative, as long aspump motor 83 operates, microcontroller 72 runs fan 74. However, whenmicrocontroller 72 deactivates pump motor 83 it also deactivates fan 74.

Control system 70 includes fill sensor 64 to provide a signal tomicrocontroller 72 that indicates when canister 19 is completely filledwith wound fluids. After receiving a signal from fill sensor 64,microcontroller 72 deactivates pump motor 83 and fan 74 and activatesalarm 95 to signal the user that canister 19 must be replaced.

Control system 70 includes switch 63 to prevent users from operatingwound closure apparatus 10 without a canister properly installed. If acanister is not properly installed, switch 63 remains open and thereforeoutputs no signal to microcontroller 72. If microcontroller 72 receivesno signal from switch 63, indicating no canister within chamber 18, itwill not supply power to pump motor 83 even after a user has pressedon/off button 78. Furthermore, microcontroller 72 activates alarm 95 tosignal the user that either a canister is not properly installed or isimproperly installed within chamber 81. Microcontroller 72 operates pumpmotor 83 only if switch 63 is depressed to provide a signal indicatingthe proper placement of a canister within chamber 18.

Control system 70 includes tilt sensor 82 to prevent operation of woundclosure apparatus 10 if it is tilted excessively. Excessive tilting ofwound closure apparatus 10 during operating diminishes the efficiency ofremoval of wound fluids and, more importantly, might result in eitherthe contamination of vacuum pump 84 or the spilling of wound fluids.Thus, if wound closure apparatus 10 tilts along any of its axes beyond apredetermined angle (approximately 45N in this preferred embodiment),tilt sensor 82 outputs a signal to microcontroller 72. In response,microcontroller 72 deactivates pump motor 83 and activates alarm 95 tosignal the user of the excessive tilt situation. In this preferredembodiment, tilt sensor 82 may be implemented with any standard mercuryswitch. A predetermined delay (e.g. 30 seconds) may be incorporated inthe circuitry so that the tilt alarm does not operate immediately.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitedsense. Various modifications of the disclosed embodiments, as well asalternative embodiments of the inventions will become apparent topersons skilled in the art upon the reference to the description of theinvention. It is, therefore, contemplated that the appended claims willcover such modifications that fall within the scope of the invention.

We claim:
 1. A porous pad for providing a reduced pressure to a tissuesite, comprising: a porous body having pores of a first averagediameter; a first outer surface covering a first portion of the porousbody and having pores of a second average diameter less than the firstaverage diameter and less than about 100 microns, wherein the firstouter surface is conformable to the shape of the tissue site; and asecond portion of the porous body for receiving and communicating thereduced pressure to the tissue site when the porous pad is inserted ontothe tissue site.
 2. The porous pad of claim 1, wherein the pores of thefirst average diameter are vacuum compatible.
 3. The porous pad of claim1, wherein the first average diameter is between about 100 and 1000microns.
 4. The porous pad of claim 1, wherein the second portion of theporous body is a second outer surface covering a second portion of theporous body.
 5. The porous pad of claim 4, wherein a portion of thesecond outer surface of the porous body overlaps a portion of the firstouter surface of the porous body.
 6. The porous pad of claim 1, whereinthe porous body is adapted to receive a tube through the second portionof the porous body.
 7. The porous pad of claim 1, wherein the firstouter surface is joined to the porous pad to form a unitary assembly. 8.The porous pad of claim 1, wherein the porous pad is fabricated from amaterial selected from the group consisting of polyurethane foam andpolyether foam.
 9. The porous pad of claim 1, wherein the pores of thefirst outer surface are formed by placing the porous pad in a liquidcoating material.
 10. The porous pad of claim 1, wherein the porous padis formed by spraying a non-toxic chemical substance into the tissuesite wherein the chemical substance foams up to conform to the tissuesite.